Fluid cooled multi-foil radiation beam window for high power beam tubes



United States Patent 3,375,387 FLUID COOLED MULTI-FOIL RADIATION BEAM WINDOW FOR HIGH POWER BEAM TUBES James E. Leiss, Gaithersburg, Samuel Penner, Potomac,

and John L. Pararas, Rockville, Md., assignors to the United States of America as represented by the Secretary of Commerce Filed Jan. 24, 1967, Ser. No. 611,478 5 Claims. (Cl. 313-44) ABSTRACT OF THE DISCLOSURE A four metal foil window with water forced between the first and second and between the third and fourth foils, and helium maintained under pressure between the second and third foils.

Field of the invention This invention relates to force-cooled, multi-foil radiation beam windows.

Description of the prior art Prior art force-cooled multi-foil windows consist of two or more closely-spaced metal foils between which a coolant is forced under pressure so as to remove the heat generated in the foils by the passage of a beam of radiation therethrough. One of the major problems associated with such windows is the tendency of the foils to burst under the high pressure of the coolant. An obvious solution to this problem is to curve the metal foils outwardly with respect to the coolant and thereby minimize the stresses induced in the foils. Unfortunately, such shaping of the foils increases the amount of coolant in the path of the radiation, and therefore increases the scattering and energy absorption of the beam. For this reason, all of the known multi-foil windows represent various compromises of the above solution: for example, the foils may be curved, with one of the foils being curved inwardly rather than outwardly with respect to the coolant, or the foils may be arranged in an essentially planar, parallel, and interconnected configuration.

Summary of the invention In accordance with the present invention, two pairs of spaced-apart outwardly-curved metal foils are utilized. The coolant is forced between each pair of foils to cool the foils, and a low-density fluid is maintained between the foil pairs, at a pressure greater than the pressure of the coolant, in order to maintain the inner foils in tension. Thus, there is interposed in the path of the radiation beam four metal foils each of minimum thickness, two thin layers of coolant, and a thick layer of low-density (low radiation absorption and scattering) fluid. In this manner, the present invention avoids the inefficient compromises that characterize the above-described prior art.

Brief description of the drawing FIGURE 1 is a front elevational view, partly in section, of an illustrative embodiment of the present invention, and

FIGURE 2 is a cross-sectional view taken on the angled line 2-2 of FIG. 1.

Description of the preferred embodiment The radiation beam window illustrated in FIGS. 1 and 2 includes a frame formed of five axially-aligned ring members 11-15. The inner diameters of the rings 11-15 are approximately equal, and thereby define a cylindrical passageway 16 for a high power beam of radiation 17 from a beam source 18, such as a linear electron accelerator or the like. Hermetically disposed across the passageway 16 are four metal foils 2124, which separate the vacuum of the beam source 18 from the atmosphere, While passing the radiation beam 17.

The foil 21 is dished and has a peripheral flange portion 26 which is clamped between rings 11 and 12. The concave surface of the foil 21 is disposed toward the interior of the passageway 16. The foil 22 is dished similar to the foil 21, and has a cylindrical extension 27 and a peripheral flange 28 that is clamped between rings 12 and 13. The extension 27 positions the dished portion of the foil 22 parallel to and a small distance from the dished foil 21, thereby forming a narrow coolant channel 30.

The foils 23 and 24 are arranged as mirror images of the foils 21 and 22. These foils 23, 24 are clamped between the rings 13, 14 and 15, and form a second narrow coolant channel 32. The concave surfaces of the foils 23, 24 face the interior of the passageway 16.

The coolant channel 30 between foils 21 and 22 carries a coolant 34 which is distributed from a manifold 35 and three tubes 36, and collected by another set of three tubes 37 and manifold 38.

The coolant 34 is also forced through the channel 32 between foils 23 and 24 via a manifold 41, tubes 42 and 43, and manifold 44. As shown in FIG. 1, the tubes 43 are connected to the coolant channel between foils 23 and 24 by means of smoothly tapered channels 45 formed in the ring 14. By experimentation, the channels 45 are shaped to provide a uniform distribution of coolant between the foils 23 and 24, to avoid localized hot portions in the foils. Although not shown, the tubes 36, 37 and 42 are provided with similar tapered transitions to their associated coolant channels.

The middle ring 13 is drilled and hermetically receives two small-diameter tubes 46 and .7. Tube 46 is utilized for admitting a low-density (low atomic number) fluid 48 into the space bounded by the ring 13 and the foils 22 and 23, while tube 47 is used for flushing air from the space, and is provided with a valve (not shown) which is closed after the air is removed from the space.

To clamp the rings 1115 together, rings 12-15 are provided with a plurality of evenly-spaced holes 50, and ring 11 is provided with a like plurality of cooperating threaded holes (not shown) for receiving machine screws (not shown) that draw rings 12-15 up to ring 11. The ring 11 is larger than the rings 12-15, and has a plurality of holes 52 adapted to register with similar holes in the beam source 18, so that the ring 11 may be secured thereto as by machine screws and nuts, indicated at 53 in FIG. 2. A conventional vacuum gasket 54 may be employed to assure a hermetic seal between ring 11 and beam source 18.

In the operation of the radiation beam window of FIGS. 1 and 2, the coolant 34 is supplied to the manifolds 35 and 41, and the low density pressurizing fluid 48 is supplied to the tube 46. The absolute pressure of the fluid 48 is always maintained greater than the absolute pressure of the coolant 34, in order to maintain the inner foils 22 and 23 in tension. After suflicient pressurizing fluid has flowed through the space between foils 22 and 23 to flush the air therefrom, tube 47 maybe closed. The radiation beam source 18 may then be activated to generate the beam 17. The heat generated in the foils 2124 by the passage of beam 17 therethrough is rapidly transferred from the foils by the coolant 34 flowing over the foils. In general, the coolant pressure is adjusted to obtain a high speed turbulent flow of coolant through the channels 30 and 32.

It will be noted that foil 21 is subjected to the vacuum of source 18 on its convex surface, and to the coolant pressure on its concave surface. Since the greater pressure is on the concave surface, foil 21 is stressed in tension. Foils 22 and 23, as noted above, are maintained in tension since the pressure of fluid 48 exceeds the pressure of coolant 34. Finally, foil 24 is maintained in tension since it is subjected to the supra-atmospheric pressure of the coolant 34 on its concave surface, and to the atmospheric pressure on its convex surface. By thus maintaining all of the dished foils 21-24 in tension, the present invention permits the foils to be formed from relatively thin stock, which minimizes the scattering and absorption of energy of the radiation beam 17.

In the preferred embodiment of the invention, the dished portions of the foils 21-24 comprise spherical portions, and the diameters of the spheres are of the same order of magnitude as the diameter of the cylindrical passageway 16. For example, if the beam passageway 16 is three inches in diameter, the foils 21-24 may have a diameter of four inches, i.e., a radius of curvature of two inches. The stresses induced in such small radius sphericallyshaped foils by the pressure differentials acting thereon are relatively low, further permitting a reduction in the thicknesses of the foils.

The preferred coolant 34 is water, although any suitable liquid or gas may be employed within the scope of this invention. The input manifolds 35 and 41 for the coolant 34 may be connected either in series or in parallel to the coolant source. If desired, the coolant may be recirculated, in the manner well known in the art.

The low density pressurizing fluid 48 may comprise hydrogen, helium, nitrogen or other low atomic number gas. The preferred gas is helium.

For the foils 21-24, copper, aluminum, aluminum alloys, stainless steel, titanium or the like may be used; in our invention the preferred foil material is titanium.

From the foregoing it will be seen that the present invention provides a radiation beam window in which the foils have maximum strength for minimum thickness, and are cooled by the high speed turbulent coolant flow. The window thus is capable of handling extremely high radiation beam currents, with a minimum of losses due to scattering, absorption and secondary radiations. The pressurizing fluid which is included in the window maintains the inner foils thereof in a strong, stable tension configuration, and does not unduly attenuate the radiation beam.

Although the present invention has been described with reference to a specific illustrative embodiment, it is to be understood that it is not limited thereto, but covers all such variations and modifications as fall within the scope of the appended claims.

We claim:

1. A radiation beam window comprising,

a frame having a cylindrical passageway for said radiation beam,

a first pair of spaced-apart dished metal foils each hermetically sealed across said passageway at one end thereof with the concave surfaces of said foils disposed toward the interior of said passageway,

a second pair of spaced-apart dished metal foils each hermetically sealed across said passageway at the other end thereof, with the concave surfaces of said foils disposed toward the interior of said passageway,

means for forcing a coolant between said first pair of foils and between said second pair of foils to cool all of said foils, and

means for maintaining a low-density fluid between the two adjacent inner foils of said pairs of foils, at a pressure greater than the pressure of said coolant, to maintain said adjacent inncr foils in tension.

2. A radiation beam window as set forth in claim 1, wherein each of said dished metal foils has the shape of a portion of a sphere.

3. A radiation beam window as set forth in claim 2, wherein each of said metal foils is titanium.

4. A radiation beam window as set forth in claim 3, wherein said coolant is liquid.

5. A radiation beam window as set forth in claim 4, wherein said low-density fluid is helium.

References Cited UNITED STATES PATENTS 2,730,637 1/1956 Atlee 31374 X 2,885,585 5/1959 Zunick et al. 31374 3,105,916 10/1963 Marker et al. 31374 X JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

